common-core-homodimer · sadekar-2006-reaction-centers

The reaction center complexes show a remarkable conservation of the core structure of 5 transmembrane helices, strongly implying common ancestry, even though the residual sequence identity is less than 10%, whereas the other proteins have structures that are unrelated. [...] Phylogenetic trees derived from the structural alignments give insights into the earliest photosynthetic reaction center, strongly suggesting that it was a homodimeric complex that did not evolve oxygen.